The present invention relates generally to orthodontic appliances and more particularly to orthodontic brackets that provide for vertical and angular adjustment, can be unrestrictively interchanged and include passive fastening means for locking the brackets securely in a desired position.
The practice of orthodontics requires the application of appliances to teeth so that they can be adjusted into proper vertical and horizontal alignment along both the upper and lower jaws of the mouth. The usual procedure has been to apply an individual metal band around each tooth, secure as by spot welding a bracket to each metal band and anchor to each bracket a continuous arch wire that would bind together all of the teeth to be straightened in the lower or upper jaw. In order to make desired adjustments to a respective tooth, it was necessary to bend or twist the arch wire in one or more directions such as vertically, inwardly or outwardly so as to retract a tooth into correct occlusion. Bending the wire is intended to accomplish proper positioning of a tooth by vertical upward or downward movement, forward or backward tipping movement and torque adjustment by rotative movement relative to the longitudinal axis of the arch wire.
In attempting to correct the position of each tooth, it is usually necessary to make a number of changes in bends or twists of the arch wire. Each bend or twist is accomplished while the wire is disengaged from respective brackets on adjoining teeth. After the bend is made and the wire is reengaged in the adjacent brackets, rotation of the wire in slots of the brackets results in undesirable tooth movement effects. In addition, each corrective bend would likely cause a reaction force in the wire secured to an adjoining or nearby tooth which in turn would require additional bending or twisting of the arch wire to obtain the desired result. Consequently, it would be difficult to achieve an absolutely correct positioning of each and every tooth in the jaw.
Various attempts to solve the problems of the prior art have been made, such as providing an anchor member welded to the metal band that surrounds the tooth and including a removable socket or channel member that has a slot for receiving the arch wire. A multitude of sockets are required, each having a different orientation of its wire receiving slot, ranging from various horizontal positions between the upper and lower extremities of the socket to any number of slot positions angled downwardly from the horizontal to an almost vertical position. This concept is disclosed in Stifter, U.S. Pat. No. 2,908,974.
In Prins U.S. Pat. No. 4,243,387 an adjustable bracket is disclosed that comprises a base member for securement to a tooth, a force receiving member and retaining means in the form of a screw. The base member and the force receiving member have respectively a concave surface and a convex surface that join together in complementary relationship and are fixed together by the screw. The force receiving member is adaptable for spherical movement on the base and is secured in a desired position by the screw. However, a large opening is required in the force receiving member in order to make spherical adjustments and maintain a particular position by intense frictional engagement by the screw.
In Karrakussoglu, U.S. Pat. No. 4,353,692 there is disclosed an orthodontic appliance that includes a complex aggregation of parts including a base member, a slidable member for movement within a recessed way of the base, a holder for receiving a bracket and frictional screw fastening means for pressing the holder and bracket against the base in a desired position. When the appliance of this disclosure is scaled to a size that may be mounted on a tooth, it is readily seen that manufacture of a screw and a threaded hole in the base would be extremely difficult and very expensive to make, if indeed, it is even possible to do so. Further, the pressure required to maintain the screw in a secured position is certain to set up forces that result in stress fractures in the slide that is intended to move along the recessed way of the base. If intense pressure of the screw is not maintained, it will likely loosen during eating and chewing activity by a patient.